The present invention relates in general to partial discharge couplers, and in particular, to partial discharge couplers for use with high voltage generator bus works.
High voltage electrical applications, such as high-voltage dynamoelectric machines, electrical generators in power plants, etc., represent capital intensive installations and typically require high availability in order to be operated in an economical manner. However, a breakdown of the insulation in such a high voltage electrical application can have significant consequences, including potential damage to the electrical device and/or components electrically coupled to the device. In this regard, proactive measures may be utilized to predict an impending breakdown. One such proactive strategy is to evaluate an indicator of the integrity of a high voltage electrical device by measuring partial discharges.
Partial discharges are small electrical sparks that occur within the insulation of electrical devices, such as windings in motors and generators. Partial discharges may also occur within the insulation of other electrical devices that are subject to high voltages, such as transformers and cables. More particularly, a partial discharge represents a localized breakdown of the electrical insulation of a component under high voltage stress. For example, localized breakdowns may occur in small air pockets within the electrical insulation. These electrical breakdowns exhibit themselves as high frequency electric current pulses that flow through the air pockets. Partial discharge measurements can be used as a predictor of reliability of the insulation of an electrical conductor, and thus a need for maintenance of the electrical device.
Accordingly, it is common to monitor power plant generators, either continuously or at regular intervals to identify the occurrence of partial discharges that could be indicative of impending component failure. In an exemplary partial discharge monitor in power plants, passive partial discharge couplers are provided on each isophase bus connecting a generator to a corresponding step up transformer. Partial discharge pulses detected by the partial discharge couplers are carried to testing equipment along corresponding signal lines for measurement and subsequent analysis.